1. Field of the Invention
The present invention relates to an aromatic polymer, and particularly to an aromatic polymer comprising a super strong acid group in side chains.
2. Description of Related Art
As membranes of electrochemical devices such as primary batteries, secondary batteries and solid polymer type fuel cells, there are used polymers having proton conductivity, namely, polymer electrolytes. For example, aliphatic polymers in which the side chain has a perfluoroalkylsulfonic acid as a super strong acid and the main chain is a perfluoroalkyl have been mainly used since they are superior in characteristics as fuel cells. However, these materials suffer from the problems that they are very expensive, low in heat resistance and low in membrane strength and cannot be practically used without making some reinforcement.
Under the circumstances, development of inexpensive polymer electrolytes substitutable for the above polymer electrolytes has recently been attempted actively. Among them, polymers comprising aromatic polyethers excellent in heat resistance and high in film strength into which sulfonic acid groups are introduced, namely, aromatic polymers having sulfonic acid groups in side chains and having aromatic main chains are considered promising. For example, polymers of sulfonated polyether ketone type (JP-A-11-502249) and sulfonated polyether sulfone type (JP-A-10-45913, JP-A-10-21943) have been proposed. However, these are still unsatisfactory in proton conductivity.
On the other hand, polymers in which the main structure is polystyrene and the side chains have perfluoroalkylsulfonic acids which are high in acid strength (JP-A-2001-302721), namely, polymers in which the side chains have super strong acids and the main chain is aliphatic, are also known, but they are insufficient in heat resistance and film strength and are desired to be improved in these properties.